Refrigerating system including auxiliary hot gas defrosting circuit



March 15, 1960 c. J. NONOMAQUE 2,928,256

REFRIGERATING SYSTEM INCLUDING AUXILIARY HOT GAS DEFROSTING CIRCUIT Fired Nov. 25, 1957 INVENTOR. 1' 2 CLYDE :r. NONOMAQUE HIS ATTORNEY United States Patent REFRIGERATING SYSTEM INCLUDING AUXILI- ARY HOT GAS DEFROSTING CIRCUIT v Clyde J. Nonomaque, Louisville, Ky., assiguor to General 7 Electric Company, a corporation of New York Application November 25, I951, Serial No. 698,462 16 Claims. (Cl. 62-156) The present invention relates to refrigerating apparatus and is more particularly concerned with a refrigerating system including an improved arrangement for employing compressed refrigerant gas to warm the evaporator component of the system to defrosting temperatures.

More specifically, this invention relates to mechanical refrigerating systems of the type including an evaporator structure for cooling an enclosure such as a refrigerator.

cabinet, a compressor unit, a condenser cooled by .the ambient air outside the enclosure, and a fixed flow restricting means, all connected in series-flow relationship. In 'the refrigerating operation of systems of .this .char- :acter, the compressor withdraws vaporized refrigerant from the evaporator structure and discharges the .compressed gaseous refrigerant to the condenser where 'it is :liquified. The compressor also forces the liquid refrigerant from-:the.condenser through the flow restricting means into the evaporator where, at a lower pressure, it is vaporized by the absorption of heat from the refrigera- 101 cabinet so as to .cool the contents .of the cabinet. During the refrigeration cycle, moisture from the air in the .cabinet collects on the evaporator in the form' of (frost. .As this frost coating has an insulating effect, it :must be removed periodically in order .to prevent .a :reduction in the operating efficiency of the refrigerating :system.

vA number of refrigerating systems Y are knownin which hot refrigerant gas is employed .for periodically heating zthe evaporator .to .defrosting temperatures. In one system' -of this type, there is provided a valve-controlled bypass line for bypassing the refrigerant flow-restricting means between the condenser and evaporator and introducing awarm gaseous refrigerant, .either directly from the com- 'pressor or from the condenser, into the same evaporator gpassages that carry .the refrigerant during the normal or refrigerating operation of .the system. The defrost operation of this type of system depends upon the thermal :storage capacity of the compressor, and the condenser if iit forms part of .the defrosting circuit, to supply .most of the heat necessary for defrosting the evaporator since z'the only other heat available is that represented by the iinput watts to the motor compressor unitwhich is.lo w rduring defrost operation due to the fact that, with the {flow restricting means bypassed, there is a substantially :unrestricted flow of refrigerant through the defrost cirrcuit so that the motor-compressor unit operates under :low load conditions. Furthermore, because the pressure aconditions existing in the evaporator during defrost operai'tion are below refrigerant condensing pressures, the refrigerant circulates through the system in the gaseous state and the latent heat of condensation of the refrig- -erant is not available for warming the evaporator. As a vresult, particularly under low ambient temperature conditions, the defrosting period may be so long as to permit an objectionable rise in temperature of any stored frozen foods thus necessitating additional control means to avoid a prolonged defrosting operation. To avoidthis 21300! performance under low ambient conditions, some ice defrost systems employ an electric heater either to heat the evaporator directly or to heat the refrigerant supplied to the evaporator. However, the use of an electric heater compressor is operating and refrigerant vaporized by the heater enters the evaporator where it condenses, giving up its latent heat of condensation and melting the frost on the evaporator. In addition to the complications of the heater, this defrost system fails to use the available stored heat and input watts to the compressor unit there by causing an uneconomical use of electricity. Also since the quantity of refrigerant flowing through the circuit is substantially increased upon energization of the heater, it is generally necessary to provide an over-sized motor compressor unit to take care of the added refrigerant circulating through the system during the defrost cycle. In still another type of hot gas defrost system, the flow of refrigerant is reversed and the evaporator receives compressed gaseous refrigerant directly from the compressor. Such a system has the disadvantages of requiring an expensive four-way valving arrangement and an oversized condenser for efiicient operation and its use has been limited generally to the commercial air conditioning and refrigeration fields.

It is therefore an object of the present invention to provide an improved arangement for the hot gas defrosting ,of .anpevaporator structure which does not require the use ofheaters, complicated valving and control components or over-size motor-compressor or condenser components and yet provides for a rapid defrosting of the evaporator structure.

Anotherobject of the invention is to provide in a refrigerating system, a hot gas defrost arrangement which permits rapid defrost oftheevaporator under both high and low ambient temperature conditions.

A further object of the invention is to provide a refrigerating system including a hot gas defrost circuit designed to employ, as the principal defrosting heat source, the input electrical energy to the compressor motor and so arranged that the electrical input to the compressor motor is high during the entire defrost operation.

Still another object of the present invention is to provide a refrigerating system including a simple and low cost hot gas defrosting arrangement which permits a quick recovery to normal operating conditions following a defrost cycle.

An additional object of the present invention is to provide in a refrigerating system, a hot gas defrost arrangement which employs the input electrical energy to the compressor motor as the primary heat source and substantially increases this input energy during defrost and which is so arranged that continued operation on the defrost cycle will not detrimentally affect the system components.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In carrying out the object of the present invention, there is provided a refrigeration system comprising a refrigerant-cooled motor-compressor unit, a condenser, a fixed flow restrictor and an evaporator connected to form a series-flow normal refrigerating circuit. Forthe purpose of periodically raising the evaporator to defrosting temperatures by means of hot. compressed refrigerant, there is provided an auxiliary circuit connected between the high and low pressure sides of the normal refrigerating circuit and in parallel with at least that part of the normal circuit including the fixed restrictor and evaporator. The auxiliary circuit includes a defrost portion in heat exchange with the evaporator and a flow restricting means between the defrost portion and the compressor having a flow restriction such that upon the operation of suitable flow control means provided in the auxiliary circuit, substantially all of the hot compressed refrigerant from the compressor flows through the auxiliary circuit and into heating'relation with the evaporator whereby condensation of refrigerant in the defrost portion, which then functions as a condenser, quickly and effectively warms the evaporator to the defrosting temperatures.

The compressor unit preferably comprises a hermetically sealed casing housing the compressor and an electric motor for driving the compressor, and the unit is connected to the remaining portions of the system in such a manner that the motor is cooled by circulating low pressure refrigerant flowing to the compressor. During defrost both the stored heat in the compressor case and the input watts to the compressor motor are employed as heat sources for defrosting the evaporator structure. Since the stored heat is quickly dissipated, the principal source of energy is that resulting from the input watts to the motor cooled by the refrigerant in the case, the case in effect being the evaporator component of the defrost circuit. This energy is transferred by the refrigerant to the evaporator structure as heat energy. In order to increase the input watts to the compressor motor during defrost operation and thereby provide a rapid defrost of the evaporator, the entire system is preferably designed so that the load on the compressor motor is higher during a defrost cycle than during a normal refrigerating cycle;'the major part of the increased load on the motor being obtained by an increase in the compressor low side or suction pressure through a transfer of most of the refrigerant charge in the system to the hermetic case during defrost operation of the system. With the compressor case functioning as the evaporator during defrost, such an increased refrigerant cooling of the compressor component is obtained during the de frosting operation that, in spite of an increased input wattage to the motor windings, there is an actual reduction in the temperature of the motor windings cooled bv the circulating refrigerant. Further, as the bypassed portionof normal refrigerant circuit is open to and in parallel connection with the auxiliary circuit during defrost operation, any abnormal rise in pressure conditions within the system resulting, for example, from controlfailure on defrost will force the normal circuit into significant refrigerating operation to oppose further pressure 1ncreases.

For a better understanding of the invention reference may be had to the accompanying drawings in which:

Fig. 1 is a diagrammatic illustration of a refrigerating system embodying the hot gas defrost arrangement of the present invention; and

2 is a diagrammatic representation of another embodrmentof the present invention.

With reference to Fig. 1 of the drawing there is illustrated a preferred embodiment of the present invention comprising the usual components of a refrigerating system including a hermetic motor-compressor unit 1, a condenser 2, a fixed fiow'restrictor 3, preferablyof' the caplllarytube type, a cooling or evaporator unit or structure 4, and a suction line 5 connected in series-flow relationship. Preferably, in accordance with the usual practice, the suction line 5 is in heat exchange with a portion of the how restrictor 3as indicatedat's. The evaporator structure '4, including an evaporatQr' circuit '6 roll-forged evaporator structure Which includes theplate or body portion .9; the accumulator 7 in such case conveniently being composed of a plurality of intersecting vertical and horizontal tubular portions in accordance with the known practices.

The motor compressor unit 1 comprises a motor 10 for driving a compressor 11, the two being sealed in a hermetic casing 12. A body of oil 14 is provided, in the lower portion of the casing 12 and is circulated within the casing by means of an oil pump (not shown) for lubricating the compressor and motor. The suction line 5 is connected to the case 12 so that the case is part of the low pressure side of the normal system and is therefore filled with low pressure refrigerant in cooling contact with the motor 10 while the compressor 11, having its inlet 15 communicating with the interior of case 12, discharges thehigh pressure refrigerantdirectly thrnugh a discharge line 16 to thecondenser In this refrigerat: ing circuit, evaporator unit components 6, 7 and case 12 form the low pressure sideof'the normal refrigerating circuit while the compressor 11 and condenser 2 comprise the high pressure side.

In a typical application of a refrigeration system of this type, the evaporator structure is placed in a cabinet (not shown) which is to be cooled, while the condenser 2 is placed in the ambient atmosphere. During the normal operation of the, refrigeration system thus far described, the refrigerant flow path is that indicated by the solid arrows in Fig. '1. The motorrcompressor unit 1 withdraws vaporized refrigerant from the top of the accumulator 7 through the suction line 5 and discharges compressed refrigerant in:a gaseous state :tothe condenser 2 where it is liquified. The refrigerant liquified in the condenser '2 passes through the capillary flow restrictor 3 into the evaporator circuit 6, where, at .a :lower pressure, it vaporizes by the absorption of heat from :the refrigerator cabinet to cool the contents .of the cabinet. Any liquid refrigerant not evaporated in the evaporator circuit 6 collects in the accumulator 7; .the connection .of the evaporator circuit 6 to the accumulator preferably being at the lower part of .theaccumulator while the suction line 5 is connected to the upper portion thereof so that, during normal refrigerating operation .of the system, only gaseous refrigerant .is withdrawn from-the accumulator through the suction line :5 by the ,motor compressor unit 1. *Since-the'line 5 is in'heat exchange at 8 with the restrictor 3, condensed refrigerant passing to the evaporator istfurther cooled 'byrthe refrigerant gas returning through the suction line.

Toaccomplish the defrostingrof the evaporator structure 4 in accordance with-the presentinvention, there is provided an auxiliary circuit 18 which is connected to the normal refrigeratingcircuit in parallel-relationship with the evaporator components 6, 7 andrestrictor -3 of the normal :circuit in such a mannerthat, along with the remaining elements of the normal refrigerating-circuit, the auxiliary circuit forms a defrost-circuit-for-the circulationof compressed refrigerant gas from the compressor into heat exchange'relationship with theevaporator structure 4for warming this structure-to defrosting temperatures.

In the embodiment of the invention shown in Fig.-1, the inlet end 19 of the auxiliary-circuit is connectedto the discharge line 16 leading from the eompressor to the condenser 2 and a normally closed valve 20' is provided for controlling thewfiow of refrigerant through the auxiliary circuit '18. The auxiliary circuit also'includesan' evaporator defrosting-portion'composed of a first secallel to the various passes of serpentine eyaporatoncircuit 6 and in heatexchange relationship therewith. The outlet end or the auxiv iary c rcuit is su ges e .t .th ...su .t. n

n by the roll-bond process.

line 5 as indicated by the numeral 24 through a restrictor tube 25 whichhas a lower flow restriction than capillary tube 3 but which provides suflicient restriction to flow of refrigerant through the auxiliary circuit to maintain the compressed refrigerant gas in defrost sections 22 and p 23 at condensing pressures.

As illustrated, the defrosting portion of the auxiliary circuit 18 comprising the section 22 and the section 23 also conveniently forms an integral part of the evaporator structure 4 when that structure is formed for example prise a separate tubular element brazed or otherwise secured to the evaporator structure 4. Also, the auxiliary circuit and evaporator circuit may be in the form of a all of the refrigerant withdrawn from the accumulator 7 v by the compressor unit 1 flows from the compressor.

through the auxiliary circuit instead of the normal refrigerating circuit. In the defrost sections 22 and 23, which correspond to the condenser component of a refrigerating circuit, the hot compressed refrigerant condenses; the liberated heat serving to melt the frost accumulated on the evaporator structure 4. The condensed refrigerant then passes through restrictor 25 and returns as a liquid or liquid-gas mixture to the compressor case 12 which functions as the evaporator on defrost. Thus the defrost circuit comprises in series-flow connection, the com-- pressor unit 1, the defrost sections 22, 23 and restrictor 25, and the flow of substantially all of the refrigerant during defrost operation is through this circuit as indicated by the broken arrows. During defrost operation, refrigerant stored in the evaporator or condenser components of the normal circuit or in both of these components is transferred to the defrost circuit where it serves to increase the load on the compressor and hence the amount of heat available from the refrigerant-cooled motor. Whenjvalve 20 is first opened, any pressure differences existing between condenser 2 and the auxiliary circuit will cause any refrigerant stored in the condenser 2 to expand and unload into the auxiliary circuit where it will condense in the defrost sections 22 and 23 and return to the case through capillary 25 causing a rapid rise in case pressure. Refrigerant vapor withdrawn from the normal evaporator structure by the compressor continuously increases the case pressure during defrost operation and this withdrawal is accelerated by the warming action of the defrost section 22 in heat exchange with the accumulator. As the case pressure increases, a greater load is placed on the motor causing the input watts to the motor to increase. The increased heat output of the motor resulting from the higher input wattage is absorbed by the refrigerant in cooling relationship with the motor and is transferred by the circulating refrigerant to the defrost section 22, 23 for defrosting of the evaporator structure.

For optimum defrost operation, the restrictor 25 is designed to restrict the refrigerant flow in the defrost circuit sufficiently to effect condensation of liquid in sections 22 and 23 but to provide a substantially higher flow rate, i.e., a lower flow restriction, for liquid refrigerant than the refrigeration capillary restrictor 3 since under defrost conditions the low side compressor pressure is higher and therefore the pumping rate in pounds of refrigerant per hour is much higher than during normal refrigeration. In addition it is not desirable to retain any substantial amount of liquid refrigerant in the auxiliary circuit ahead of re- Alternatively, it may comtion of the refrigerant in the defrost sections at increasingly higher pressures. The liquified refrigerant from the defrost sections is subjected to a pressure reduction as it flows through the restricting tube 25 and enters the compressor case at a lower pressure producingrefrigeration in the case. This refrigeration overcomes the heating effect of the increased input watts to the motor 10 and actually causes the temperatures of the entire compressor unit 1 including the body of oil 14 to decrease substantially. All of this heat energy is quickly removed from the motor compressor by'the circulating refrigerant and is made available for defrosting of the evapoartor 4. When the defrosting is complete, valve 20 is closed and the system is immediately returned to a normal refrigeration on cycle.

iFor automatically initiating defrost operation of the system, there may be employed a suitable electrical control circuit which periodically energizes a solenoid 29 to open valve 20 and effectflow of gaseous refrigerant from I the high pressure side of the system through the auxiliary circuit; An electrical control circuit suitable both for this purpose and for controlling normal operation of the system is illustrated in Fig. 1. For normal refrigerating control, the circuit comprises a pair of supply lines or condoctors 30 and 31 for energizing the compressor motor 10 through a temperature-operated switch 32 in supply line 30. A temperature sensing'device 33 in contact with the evaporator structure 4 operates switch 32 so that during normal operation of the system the compressor motor isenergized, for example, whenever the evaporator structure reaches a predetermined maximum temperature of 0 F. and de-energized when the structure attains a predetermined low temperature of .20 F.

The defrost control portion of the electrical circuit comprises a defrost control switch 34 for periodically energizing solenoid 29; the switch 34 and solenoid 29 being connected in series to supply lines 30 and 31 in such a manner that the energization of solenoid 29 is also under control of switch 32. Defrost control switch 34 can be any of the known switch means designed to close the circuit to solenoid 29 as a function of time, number of refrigerator cabinet door openings or the like and to open when the temperature sensed by a temperature sensing element 35 contacting the evaporator structure 4 is a few degrees above freezing, i.e., such that the evaporator structure has reached a frostfree condition.

It will be seen that this electrical control circuit is designed to permit energization of the solenoid 29 to open valve 20 onlywhen the switch 32 is also closed to energize compressor motor 10 so that the valve 20 will open only if the compressor is also energized. Once the defrost cycle is initiated, the sensing device 33 will sense only higher evaporator temperatures. Switch 32 will, therefore, remain closed and the compressor will operate continuously during the entire defrost cycle and a normal refrigerating cycle immediately following the defrost cycle; the defrost cycle being terminated and the refrigerating cycle initiated by operation of switch 34 when the sensing device 35 indicates that the evaporator is free of frost. Switch 32 will open to stop the compressor only when the sensing device 33 again senses the predetermined low evaporator temperature of, for example, -20 F.

In the event a fan is employed for forced draft cooling of the condenser 2, it is desirable that the fan be tie-energized during the. defrosting operation to minimize condensation of refrigerant in the condenser. The operation of a condenser fan, indicated by numeral 37, can conveniently be controlled also by switch 34 in such a manner that the fan motor is energized only when the compressor is energized and the solenoid 29 is de energized.

It will be noted that during the operation of the system of the present invention on the defrost cycle, no

positive means are provided for prohibiting flow of reis ran h u h e ormal. refrigerating irc i h is, h ou h, e ense 1 ca il ry 3, and, e e ts passage 6 and accumulator 7. While a small amount of gas continues to flow to the condenser and through the normal circuit, it has no significant effect on the defrosting function because the flow rate through the auxiliary cuit 8 h ch h s a e ser r s e t efr erant flow than the normal refrigerating circuit, is much larger.

While the flow restriction or resistance in the auxiliary circuit 18 as provided primarily by the restrictor 25 s p n it ll, b under ood hat the re uir Icstriction provided in this circuit as well as the'total refrigerant charge for the refrigerating system will be govm to a r e exten b t e desi o l o h c mp ne t Par s T kin ne h u eho d r f r t m f h e how i'E 1 s an x m s fa y ef r t and. frost rzsrfctman was tai e b using a charge of from I} to 17 ounces of Freou. .l2" refrigerant. The accumulator 7 in the normal circuit had a refrigerant storage capacity of about two-thirds of the charge. A standard capillary having a 0.225 cubic foot per minute flow rate for dry nitrogen at 100 p.s.i.g. was employed as restrictor 3 and the restrictor 25 was dimensioned to have a flow rate of 1.8 cubic feet per minute for dry nitrogen at 100 p.s.i.g. for a horse power compressor and 1.40 cubic'feet per minute, for a horsepower compressor. In tests on this system, it

was found that the fiow rate of the restrictor 25 was not,

extremely critical between flow rates of 1.2 and 3.2 cubic feet per minute and that a restriction within this. range would satisfy the thermodynamic principles of temperature and pressure for refrigerant condensation although optimum sizing provided minimum defrosting time.

In general, for best performance of systems in which there is no substantial pressure drop except across the restrictors 3 and 25, it has been found that the restriction of the auxiliary circuit restrictor 25 should be about onefifth to one-tenth the restriction ofiered by the capillary tube 3. A ratio of about 1 to 8 gave excellent results in the above-described system employing a horsepower compressor. Decreasing the flow rate through the auxiliary circuit causes liquid refrigerant to be held in the defrost circuit sections 22 and 23 so that less refrigerant is available to the compressor case for raising the case pressure and increasing the heat available from the input Watts to the compressor motor 10. Higher flow rates of refrigerant through the auxiliary circuit 18 can be tolerated substantially without harm as the system will still function except that it will take slightly longer to reach condensing pressures in the defrost sections and therefore a longer time will be required to defrost the evaporator structure. The limit in this direction is the point at which only gas will be circulated without .condensing in the defrost sections.

Systems constructed in accordance with the present invention to meet the above-illustrated specifications have operated successfully to defrost an evaporator structure such as that illustrated in Fig. 1 within a matter of a few minutes, generally less than minutes, even under low ambient conditions of about 60 F. whereas comparabie systems, differing only in the fact that the defrosting of the evaporator was obtained by merely bypassing the normal refrigeration capillary and introducing compressed refrigerant directly from the condenser into the evaporator, required at least 4.5 minutes to defrost the same evaporator structure in a 60 F. ambient.

Actually, the system of the present invention defrosts the evaporator almost as rapidly in a 60 ambient as in a 100 ambient. The principal reason. for this is, that the defrosting operation is effected primarily by the heat energy obtained from the increased input watts to the compressor motor during the defrost operation and only to a minor extent by; the heat stored in the compressor ase f om a Pre us norm r a in y l n. this connection, it should be noted that while the input watts to the compressor and he ce, the, amount of heat available from this sourceisgoyerned by both the high and low side pressures, the larger influence is the low side pres:

sure which primarily determines, the amount of refrigerant to be compressed by the compressor during each stroke. For example, where the case or low side pressure in a given system was 19.19 p.s.i.a. (minus10' F. exaporator temperature), an increase in head pressure from 50 p.s.i.g. to150 p.s.i.g. caused the watts input to the motor to rise from 255 wats to 274 watts. Thus, an increase of only 19 watts are obtained for a p.s.i.g. head pressure in-. crease. .On the other hand, changing the low side or suctiou pressure from 19.19 to 35.7 p.s.i.a. (corresponding to: 'l0 F. to +20 F.) providedv a 354. watts input at 50 p.s.i.g. head pressure and 400 watts at p.s.i.g. head pressure. In other words, an increase in the low de p ur o -51 P-fi-ica se a wat a e nc s ranging from 99 to 126 watts. Thus it is seen that sub-v stantially more heat is available for defrosting purposes with a given increase in low side pressure. This desirable increase in low side pressure during defrost is accomplished in accordance with the present invention by transferring refrigerant normally stored in the main refrigerant circuit to the defrost circuit.

Describing further the operating characteristics of the system of the present invention, it has been found that as defrosting progresses, the temperature ofthe evaporator increases due to the condensation of refrigerant-"in Y the defrost circuit at increasingly higher pressures in that circuit. At the same time, condensed refrigerant. passing into the compressor case produces refrigeration at the lower pressure conditions prevailing therein. This refrigeration in the case, causes the compressor unit 1 including the oil 14 to reduce in temperature in spite of the fact that more heat is being generated in the case due to the increasing input watts to the windings of the motor 10. Because of the increased refrigeration in the case, this heat energy is quickly removed from the compressor case and transferred to the evaporator structure 4 for defrosting use.

While the normal refrigerating circuit is open to the compressor during defrost, the flow of refrigerant through the capillary 3 and through the normal refrigerant evaporator circuit fi'during defrost is extremely small. One reason for this is the difference in the designed flow rates of the two restrictors 3 and 25. The other is the fact that during defrost the refrigerant at the inlet to capillary 3 is normally in the gaseous state while the refrigerant flowing through restrictor 25 is, at least partly, in the condensed or liquid phase. Circulation of refrigerant through the main refrigerating circuit during the defrost cycle can be further minimized if the outlet end of restrictor 25 is connected into the suction line as at 24 between the point 8, Where the normal refrigerating suction line and normal capillary 3 are in heat exchange, and the compressor. This arrangement prevents the liquid refrigerant leaving the defrost system from sub-cooling the refrigeration capillary 3 and increasing the flow rate through this capillary. It will be obvious, of: course, that outlet point 24 could be on the low side of the compressor case to introduce returned refrigerant fromthe auxiliary te- 18 i ect y nt t e ca e i As is the casewith all fixed restrictor systems, the optimum operation of the present system will also depend on the refrigerant charge. In determining the optimum charge, consideration should be given the system conditions existing during defrost. In this connection, it will be seen that both of the restricting capillaries 3. and 25 have approximately the same high and low pressures during fr s The onden rl n he. auxi ar ci u t upto'the restrictor 25 comprise, a common pressurev side, while the common low pressure side includes the c mpr s or. c se. the s p nt n e apor or he. 1

condensing in sections 22 and 23 of the auxiliary circuit. Hence, the preferred total charge for defrost would be the quantity necessary to supply gas to all of the-componentsof the system other than the compressor case,

plus that required in the case to produce the desired rise in case pressure and to compensate for the amount of refrigerant absorbed by the oil 14 which, for some refrigerants, such as'Freon-12, is constantly increasing as the case temperature is lowered. A component of the normal refrigerating circuit, such as the accumulator 7, can then be designed to store any difference between the total charge desired for defrost and that required for best refrigerating performance of the system when valve is closed. Thus it will be seen that the present invention employs a defrost circuit of smaller effective volume, i.e., having. a lower liquid storage capacity than the normal circuit and preferably takes advantage during defrost of reserve refrigerant normally stored in the low pressure side of the normal circuit to increase the case pressure and to compensate for the loss of the refrigerant dissolved in the oil as the temperature of the oil decreases during the defrost cycle.

While a particular advantage of the present invention is a rapid defrost operation, in some applications it may be desirable to provide a slower rate of defrost and at the same time retain some of the other major advantages of the invention such as the increased load on the compressor during the defrost cycle. Such a system is shown in Fig. 2 of the drawing in which the same reference numerals are employed to indicate elements having the same or similar functions. In the system of Fig. 2, the flow of refrigerant through the auxiliary circuit 18 is in the same direction as the flow of refrigerant through the parallel passes of the evaporator 6 rather than countercurrent as in the modification of Fig. 1 and the auxiliary circuitlS has its inlet end connected to the discharge end of the condenser 2. Either one or both of these changes will decrease the rate of defrostof the evaporator structure 4 which in this modification is shown as comprising the tubular. evaporator circuit 6, an accumulator 7 and defrost section 41 brazed or otherwise secured to plate 9.

Since in the defrost operation of the system of Fig. 2, the hot gas flowing through the auxiliary circuit 18 upon operation of the valve 20 first contacts the serpentine evaporator. 6 and then the accumulator 7, the accumulator in this case is the last to be heated by the defrost gas. Thus the liquid refrigerant stored in the ac cumulator during normal refrigeration will vaporize more slowly than in the modification shown in Fig. 1 so that its return to the compressor, where it raises the low side pressure and the corresponding input watts to the motor, is slower. The rate of defrost is therefore somewhat slower. By connecting the auxiliary circuit to the condenser outlet as indicated at 43, the hot gas from the compressor passes through the condenser 2 before entering the auxiliary circuit 18. As the defrost gas will lose its superheat in.

the condenser, there is thus a loss of total heat energy to ambient and therefore less total heat energy will be available for the defrosting of the evaporator structure 4.

.It will'be obvious, of course, that either one or both of these means may be employed for obtaining a slower rate of defrost than that obtainable with the system of Fig. l, and the selection will depend upon the system application. If only one is employed, it should be noted that the inclusion of the condenser in the defrost circuit permits a continued loss of heat energy to ambient thereby decreasing the maximum defrost temperatures obtainable at the evaporator structure. The refrigerant flow through the auxiliarycircuit as provided by the system of Fig. 2 causes slower vaporization of the refrigerant stored in accumulator 7 and hence lengthens the defrost period primarily because the low side compressor pressure is increased at a slower rate. However, it has no significant effect on the maximum evaporator temperatu r'e's available for defrost once {all of the stored refrigerant has been transferred to the compressor case.

In this or in the embodiment of the invention as shown in Fig. l, a sump or receiver 42 may be provided between the defrost section 41 and the restrictor 25 to increase thecapacity of the auxiliary circuit if, for example, the normal. refrigerating circuit requires a larger refrigerant charge than can be handled by the compressor case during defrost. The provision of a receiver 42 will also provide a slower defrost rate.

An added advantage of the present invention, which is characteristic of both embodiments as illustrated in Figs. 1 and 2, results from the fact that the normal refrigerating circuit is open and is directly connected to the auxiliary circuit during the defrost operation. By this arrangement, it is unnecessary to provide any control means as over-temperature or over-pressure protection in the event, for example, that valve 20 remains open and the compressor continues to operate after the evaporator structure has been completely defrosted. As

to the self-protecting operation of the system, it will be noted that during the early stages of defrost, refrigerant is continuously condensing in the sections of the auxiliary circuit heat exchanging the evaporator so that there is no immediate pressure build-up of any significance in this part of the auxiliary circuit. While the system pressure increases somewhat as defrost continues and the evaporator temperature increases, the pressure in the high side of the complete system (ahead of the restrictors in the normal and auxiliary circuits) and particularly in the condenser 2 may ultimately become sufficient to elfect condensation of refrigerant in the, condenser. Under normal circumstances complete defrosting of the evaporator structure is obtained by this time so that the controls return the system to normal operation. However, continued operation on the defrost cycle beyond this point is not injurious since upon condensation of refrigerant in the condenser, restrictor 3 will feed liquid refrigerant to the evaporator structure. With this concurrent refrigeration in the normal circuit, the system pressure will rise at a continuously deceasing rate as the two parallel circuits are then working against one another temperature-wise 'so that neither the evaporator structure nor the motor-compressor unit including the motor windings will be detrimentally afiected even though the system continues to operate on the defrost cycle after the evaporator has reached defrosting temperatures.

The hot gas defrost system of the present invention is 7 also characterized by economical and rapid defrosting,

1 that the invention is not limited to these particular forms and it is intended by the appended claims to cover all modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United'States is:

l. Ina refrigerating system of the type comprising a compressor, a condenser, a fixed flow restrictor and an evaporator connected in series-flow refrigerating circuit, means for defrosting said evaporator comprising an auxiliary refrigerant flow circuit connected to said refrigerating 1 l circuit in parallel refrigerant flow relationship with said fixed flow restrictor and evaporator and including a defrost portion in heat exchange relationship with said evaporator, said auxiliary circuit being connected at its inlet end to said refrigerating circuit between said compressor and said restrictor and at its outlet end to said refrigerant circuit between the outlet end of said evaporator and said compressor, normally closed valve means in said auxiliary circuit for normally preventing flow of compressed refrigerant through said auxiliary circuit said auxiliary circuit including flow restricting means for maintaining condensing pressures in said defrost portion during flow of refrigerant through said auxiliary circuit, said flow restricting means having a lesser effective flow restriction than said fixed flow restriction whereby substan tially all of the compressed refrigerant from said compressor flows through said auxiliary circuit when said valve means is open.

2.. In a refrigerating system of the type comprising a compressor, a condenser, a fixed flow restrictor and an evaporator connected in series-flow refrigerating circuit, means for employing compressed refrigerant for defrosting. said evaporator comprising an auxiliary refrigerant circuit having a portion in heat exchange relationship with said evaporator and connected at its inlet end to said refrigerating circuit between said compressor and said restrictor and at its outlet end to said refrigerating circuit between said evaporator and said compressor, a normally closed valve in said auxiliary circuit for normally preventing flow of compressed refrigerant through said auxiliary circuit, and flow restricting means in said auxiliary circuit for restricting fiow of compressed refrigerant from said heat exchange portion to said compressor, said flow restricting means having a higher flow rate than said fixed flow restrictor whereby substantially all the compressed refrigerant from said compressor flows through said auxiliary circuit when said valve is open.

3. A refrigerating system comprising a compressor, a condenser, a fixed flow restrictor and an evaporator connected in series-flow refrigerating circuit whereby said compressor normally withdraws low pressure refrigerant from said evaporator and discharges high pressure refrigerant to said condenser, a motor for driving; said compressor and disposed in heat exchange relation with said low pressure refrigerant for cooling thereby, means for periodically defrosting said evaporator comprising an auxiliary circuit having a portion in heat exchange with said evaporator, a fiow restricting means in said auxiliary circuit following said portion, a normally closed valve in said auxiliary circuit, and means connecting said auxiliary circuit to said refrigerating circuit ahead of said condenser to permit series flow of refrigerant from said compressor through said heat exchange portion, said flow restricting means, in cooling contact with said motor, and back to said compressor when said valve is open, and refrigerant storage means for storing a portion of the refrigerant charge in said system as a liquid during said normal operation thereof and for releasing said excess charge upon opening of said valve to increase substantially the load on said compressor when the refrigerant flow is through said auxiliary circuit.

4. A refrigerating system comprising a compressor, a condenser, a fixed restrictor and an evaporator connected in series-flow refrigerating circuit; whereby said compressor normally withdraws low pressure refrigerant from said evaporator and discharges high pressure refrigerant to said condenser, a motor for driving said compressor and disposed in heat exchange relation with said low pressure refrigerant. for cooling thereby, means for periodically defrosting said evaporator comprising an auxiliary circuit having a portion inheat exchange with said evaporator, a flow restricting means in said auxiliary circuit following said' porti on, and means connecting said auxiliary circuit to said refrigerating circuit for series flow of refrigerant from said compressor through said heat exchange portion, said flow restricting means, in cooling contact with said, motor and back to said compressor, a normally closed valve for controlling flow of refrigerant to said auxiliary circuit, a charge of refrigerant in said system greater than that required for normal refrigerating operation thereof, and means in said refrigerating circuit and in heat exchange. with said auxiliary circuit for storing the excess charge during said normal operation and for releasing said excess charge upon opening of said valve to increase substantially the load on said compressor when the refrigerant flow is through said auxiliary circuit.

5. A refrigerating'system of the type comprising a compressor, a condenser, a restrictor and an evaporator connected in normally closed series-flow refrigerating circuit and means for defrosting said evaporator comprising an auxiliary circuit hzwing a portion in. heat exchange relationship with said. evaporator, said. auxiliary circuit being connected at its inlet end to said refrigerating circuit between said compressor and said restrictor andv at its outlet endyto said refrigerant circuit between said evaporator and said compressor, valve means operable to permit the flow of compressed refrigerant gas from said compressor through said auxiliary circuit, and a second restrictor in said auxiliary circuit between said heat exchange portion and said. outlet end for maintaining refrigerant condensing pressures in said auxiliary circuit portion when refrigerant is flowing therethrough, said second restrictor having. a flow restriction of from about one-fifth to one-tenth that of said refrigerating circuit restrictor.

6. A refrigerating system comprising a. compressor, a condenser, a fixed restrictor and an evaporator connected in series-flow refrigerating circuit whereby said compressor normally withdraws low pressure refrigerant from said evaporator and discharges high pressure refrigerant to said condenser, 21 motor for driving. said compressor and disposed in heat exchange relation with said low pressure refrigerant for cooling thereby, means for periodically defrosting said evaporator comprising an auxiliary circuit having a portion in heat exchange with said evaporator, a flow restricting means in said auxiliary circuit following said portion, said flow restricting means having a flow restriction of from about one-fifth to one-tenth that of said fixed restrictor, and means connecting said auxiliary circuit to said refrigerating circuit for series flow of refrigerant from said compressor through said heat exchange portion, said. flow restricting means, in. cooling contact with said motor and back to said compressor, a normally closed valve for controlling flow of refrigerant to said auxiliary circuit, a charge of refrigerant in said system greater than that required for normal refrigerating operation thereof, and means in said refrigerating circuit for storing the excess charge during said normal operation and for releasing. said excess charge to increase substantially the. load. on said compressor upon opening of saidvalve.

7. A.refrigerating, system comprisinga compressor, a. condenser, a restrictor, an evaporator and a refrigerant accumulator connected in series-flow refrigerating circuit whereby said compressor normally withdraws low pressure gaseous refrigerant from'said accumulator and discharges high pressure refrigeranttosaid condenser, a drive motor for said compressor, av hermetic casing enclosing said compressor. and saidmotor, said. motor being arranged to becoolediby lowpressure refrigerant flowing to said compressor, said accumulator normally storing a portion of the refrigerant charge in the liquid state, means for periodically defrosting said evaporator comprising an auxiliary circuithaving a portion in heat exchange with said evaporator and said accumulator, and valve-controlled meansfor-elfecting substantially unrestricted flow of'high pressure refrigerant from said-compressor to said heat,

exchange portion of:said.auxiliary circuit, said auxiliary circuit having an outletend connected to said refrigerat- I 13 l ing circuit between said accumulator and said compressor and including a flow restricting means between said heat exchange portion and said compressor for maintaining condensing pressures in said heat exchange portion, warming of said accumulator by said heat exchange portion causing said stored refrigerant to be discharged from said accumulator and into cooling relationship with said drive motor upon operation of said valve-controlled means.

8. A defrostable refrigerating system comprising an evaporator structure including a refrigerant evaporator passage and a liquid refrigerant accumulator, a compressor, a condenser and a capillary flow restrictor, conduit means including a suction line between said accumulator and compressor connecting said compressor, condenser, capillary flow restrictor, evaporator passage and accumulator in series-flow refrigerating circuit whereby' said compressor normally withdraws low pressure refrigerant from said accumulator through said suction line and discharges high pressure refrigerant to said condenser, a portion of said suction line being in heat exchange relation with said capillary flowrestrictor, and means for periodically raising said evaporator structure to defrosting temperatures by means of compressed gaseous refrigerant from said compressor comprising an auxiliary circuit having its inlet end connected to said refrigerating circuit between said compressor and said capillary flow restrictor and its outlet end connected to the low pressure portion of said refrigerating circuit between the point at which said suction line is in heat exchange with said capillary flow restrictor and said compressor, said auxiliary circuit including a defrost portion in heat exchange relation with said accumulator and said evaporator passage for warming said accumulator and said evaporator passage, a normally closed valve in said auxiliary circuit for normally preventing flow of compressed refrigerant to said auxiliary circuit, said auxiliary circuit including a fiow restricting means between said defrost portion and said compressor for restricting the flow of refrigerant to said compressor thereby to maintain refrigerant in said defrost portion at condensing pressure conditions when said valve is open to permit compressed refrigerant to enter said auxiliary circuit, the flow restriction of said auxiliary circuit flow restricting means being less than the flow restriction provided in said refrigerant circuit by said capillary flow restrictor whereby, when said valve is open, substantially all of the circulating refrigerant flows through said auxiliary circuit.

9. The defrostable refrigerating system of claim 8 in which the refrigerant charge in said system is greater than that required for normal refrigerating operation, at least part of the excess refrigerant being stored as a liquid in said accumulator during normal operation of the system and being discharged therefrom to increase the load on said compressor when said accumulator is warmed by compressed refrigerant flowing through said defrost portion.

10. A defrostable refrigerating system comprising an evaporator structure including an evaporator passage and a liquid refrigerant accumulator, a hermetic compressor unit including a sealed casing and a compressor and a motor for driving said compressor disposed within said casing, said compressor having "an inlet port communicating with the interior of said casing, a condenser and a capillary flow restrictor, conduit means connecting said compressor, condenser, capillary fiow restrictor, evaporator passage, accumulator and casing in closed series-flow refrigerating circuit whereby said compressor withdraws low pressure refrigerant from said casing and discharges high pressure refrigerant to said condenser, said motor being cooled by low pressure refrigerant in said casing, and means for periodically raising said evaporator structure to defrosting temperatures by means of hot compressed refrigerant from said compressorcomprisingan auxili'ary'circuit having its inlet connected to said refrigerant circuit between said compressor and said condenser and its outlet connected to said refrigerating circuit between said accumulator and said compressor, said aux iliary circuit including a defrost portion in heat exchange relation with said accumulator and said evaporator passage, a normally closed valve in said auxiliary circuit for controlling the flow of compressed refrigerant to said auxiliary circuit, said auxiliary circuit including a flow restricting means between said defrost portion and said compressor for restricting the flow of refrigerant to said compressor thereby to maintain refrigerant in said defrost portion at condensing pressure conditions when said valve is open, the total flow restriction of said auxiliary circuit being less than the flow restriction provided in said refrigerant circuit by said capillary flow restrictor whereby when said valve is open substantially all of the compressed refrigerant from said compressor flows through said auxiliary circuit.

11. A defrostable refrigerant system comprising an evaporator structure including a refrigerant evaporator passage and a refrigerant accumulator for normally storing in liquid form a portion of the refrigerant charge in'said system, said accumulator being connected to the outlet end of said passage, a hermetically-sealed motorcompressor unit including a compressor and a motor for driving said compressor disposed within a sealed casing, acondenser, and a capillary flow restrictor, conduit means including a suction line between said accumulator and said casing connecting said compressor, condenser, capillary flow restrictor, evaporator passage, accumulator and casing in closed series-flow refrigerating circuit whereby said compressor witthdraws low pressure refrigerant from said accumulator through said suction line and sealed casing and discharges high pressure refrigerant to said condenser, said motor being cooled by low pressure refrigerant passing through said casing, and means for periodically raising said evaporator structure to defrosting temperatures by means of hot compressed refrigerant from said compressor comprising an auxiliary circuit including valve means for controlling flow of refrigerant therethrough, said auxiliary circuit having its inlet end connected to said refrigerating circuit between said compressor and said restrictor and its outlet end connected to the low pressure portion of said refrigerating circuit between said accumulator and said compressor, said auxiliary circuit including a first defrost section in heat exchange relation with said accumulator and a second defrost section extending generally parallel to said evaporator passage in heat exchange relation therewith, and a flow restricting means having a flow restriction less than that provided by said capillary fiow restrictor, said compressor, first defrost section, second defrost section, flow restricting means and casing forming a defrost circuit for flow of compressed refrigerant from said compressor to said defrost sections when said valve is open, said casing forming the low pressure side of said defrost circuit, said accumulator being adapted to discharge to the casing the liquid refrigerant normally stored therein when heated by hot compressed refrigerant in said first defrost section thereby to increase the load on said compressor motor and increase the amount of heat absorbed from said motor by the circulating refrigerant in said casing.

12. A defrostable refrigerating system comprising an evaporator structure including a serpentine evaporator passage and a liquid refrigerant accumulator, a hermetically sealed motor-compressor. unit including a motor and a compressor disposed in a sealed casing, a condenser, and a capillary flow restrictor, conduit means including a suction line between said accumulator and said casing connecting said compressor, condenser, capillary flow restrictor, evaporator passage and accumulator in closed series-flow refrigerating circuit whereby said compressor normally withdraws low pressure. gaseous refrigerant from said accumulator through said suction line and.

gees-ass sealed casing and discharges high pressure refrigerant to said condenser, a portion of said suction line being in heat exchange relation with said capillary flow restrictor, said motor being cooled by low pressure refrigerant in said casing, and means for periodically raising said evaporator structure to defrosting temperature by means of hot compressed refrigerant from said compressor comprising an auxiliary circuit having its inlet connected to said refrigerating circuit between said compressor and said capillary flow restrictor and its outlet connected to the low pressure portion of said refrigerating circuit between the point at which said suction line is in heat exchange with said capillary flow restrictor and said compressor, said auxiliary circuit including in series connection a normally closed valve adjacent said inlet to said auxiliary circuit, a defrost portion in heat exchange relation with said accumulator and said evaporator passage, and a flow restricting means for restricting the flow of refrigerant from said defrost portion to said compressor thereby to maintain refrigerant flowing through said defrostportion at condensing pressure conditions when said valve is open, the flow restriction of said auxiliary circuit being less than the flow restriction provided in said refrigerant circuit by said capillary flow restrictor whereby upon operation of said compressor with said valve open substantially all of compressor gaseous refrigerant from said compressor flows through said auxiliary circuit at a rate of flow that is greater than the normal flow rate through said refrigerating circuit.

1.3. A refrigerating system comprising a hermetic compressor unit including a casing and a compressor and a motor for driving said compressor within said casing, a condenser, a fixed flow restrictor and an evaporator, conduit means connecting said compressor, condenser, fixed flow restrictor, evaporator and casing 'to form a closed series-flow normal refrigerating circuit in which said compressor withdraws low pressure refrigerant from said evaporator and through said casing and discharges igh pressure refrigerant to saidcondenser, said motor being cooled by the low pressure refrigerant in said casing, means for periodically Warming said evaporator to defrosting temperatures comprising an auxiliary circuit having its inlet end connected to said normal refrigerating circuit between said compressor and said fixed flow restrictor and its outlet end connected to said normal refrigerating circuit between said evaporator and said compressor, said auxiliary circuit including a defrost portion in heat exchange relation with said evaporator and a flow restricting means, conduit means connecting said compressor, said defrost portion, said flow restricting means and said casing to form a series-flow defrosting circuit, a normally closed valve in said auxiliary circuit for controlling flow of refrigerant throughsaid auxiliary circuit, the flow restriction provided by said flow restricting means in said auxiliary circuit being sufficient to maintain condensing pressures in said defrost section when refrigerant is flowing through said defrost section but being substantially less than the flow restriction motor for driving said" compressor disposed withinsaid casing, said compressor having an inlet'port corn'muni eating with theinterior of said'casing, a condenser and i a t A I I .r a capillary flow restrictor, conduit means including a suction line between said accumulator and compressor casing connecting said comprssor, condenser, capillary flow restrictor, evaporator passage, accumulator and casing in closed series-flow refrigerating circuit whereby said compressor withdraws low pressure refrigerant from said casin-gand discharges high pressure refrigerant to said condenser, said motor beingcooled by low pressure refrigerant in said casing, and means for periodically raising said evaporator structure to defrosting temperatures by means of hot compressed refrigerant from said compressor comprising an auxiliary circuit having its inlet connected to said refrigerant circuit between said condenser and said capillary flow restrictor and its outlet connected to the low pressure portion of said refrigcrating circuit between said vaccumulator and said compressor inlet port, saidauxiliary circuit including a first section extending gener'allyparallel to said evaporator passage in heat exchange relation therewith, and a second section in heat exchange with said accumulator, a normally closed valve in said auxiliary circuit for controlling the flow of compressed refrigerant to said auxiliary circuit, said auxiliary circuit including a flow restricting means between said' second section thereofand said compressor for restricting the flow of refrigerant to said compressor thereby to maintain refrigerant in said sections at condensingpres'sure conditions, the total flow restriction of said auxiliary circuit being less than the flow restriction provided in said refrigerant circuit by said capillary flow restrictor whereby when said valve is open substantially all of the compressed refrigerant from said compressor flows through said auxiliary circuit. 15. In a refrigerating system of the type comprising a compressor, a condenser, 21 restrictor and an evaporator connected in series-flow refrigerating circuit, a motor for driving said compressor, means for employing compressed refrigerant for defrosting said evaporator comprising an auxiliary refrigerant circuit having a portion in heat exchange relationship with said evaporator and connected at its inlet end to said refrigerating circuit between said compressor and said restrictor and at its outlet end to said refrigerating circuit between said evaporator and refrigerant through said auxiliary circuit, flow restricting means in said auxiliary circuit for restricting flow of compressed refrigerant from said heat exchange portion to said compressor, temperature controlled switch means foroperating said motor responsive to evaporator temperature, control means to open said valve for defrost operation of said system only when said temperature controlled switch means is actuated to operate said motor, and means-to close said valve when said evaporator has been defrosted whereby a defrost operation is immediately followed by refrigerating operation of said system.

16. A refrigerating system comprising a compressor, a condenser, a fixed flow restrictor and an evaporator connected in series-flow refrigerating circuit whereby said compressor normally withdraws low pressure refrigerant from said evaporator and discharges high pressure refrigerant to said condenser, a motor for driving said compressor and disposed in heat exchange relation with said low pressure refrigerant for cooling thereby, means forperiodically'defrosting saidevaporator comprising an auxiliary circuit having a defrost portion in heat exchange with said evaporator, a normally closed valve in said auxiliary circuit, means connecting said auxiliary circuit to said refrigerating circuit ahead of said fixed flow restrictor to permit series flow of refrigerant from said compressor through said heat exchange portion, in cooling. contact with said motor, and back to said compressor when said valve is open, and flow restricting means in said auxiliary circuit for maintaining condensing-pres through said auxiliary circuit, said flow rcstrictingmean having a higher flow rate than said fixed flow restrictqif 1 whereby substantially all 05 the compressed refrigerant? from said compressor flows through said auxiliary circuit upon opening of said valve.

UNITED STATES PATENTS Warren June 14, 1932 Kucher May 11, 1937 Zearfoss Aug. 10, 1954 Kundan Aug. 21, 1956 

